need a site finished php/mysql

we have a site that needs to be finished off, it is mostly functioning but there are 4 items that need to be addressed

1. when information is submitted for a date that already exists nothing happens in the database, the original value remains, and the user is told it was successful in adding the information, we need a check for already existing dates and display a warning telling the user the date already exists and that they need to edit it instead

2. everytime information is submitted an email is supposed to be generated, it does not send email everytime this seems to be related to the problem above, I am sure that when the above point is resolved this will fix itself

3. multiple users at one time are causing problems as all of the information does not seem to be getting added to the database

4. the calendar portion does not highlight dates that already have events, we need to have the dates highlighted

items 1, 2 and 3 are the most important to have fixed, we already have the pages so we are just looking for someone to finish off the programming based on the code we already have

this needs to be completed by June 1st, 2009 so I will be choosing someone today (May 28th, 2009)